Hello all, most of my cars are American muscle so forgive if this is a silly question but in detailing my 356 engine bay, these tubes circles go to nothing .. runs fine and I’m guessing I have a custom exhaust. Should they be vended and what are they ?
thanks
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Those are manifold heat tubes for single carb applications. They run between the number 2 and number 4 exhaust flanges, and are meant to keep the manifold from icing. It's the same idea as circulating coolant under the manifold of a V8.
What Stan said- without an exhaust manifold to bolt to (and a wee bit of exhaust to circulate through- with an aftermarket header you usually have to drill a small hole into the header tubing through the flanges at each end) the center mounted carburetor can ice up in less than ideal weather- you'll know it's happening when the engine suddenly won't run right below about 3,000 rpm. If you run around to the back of the car quickly you even may see frost on the manifold directly below the carb. It's not the best design and dual carburetors are infinitely better, but VW was thinking about costs (the Beetle was an economy car) and the single carburetor with long intake runners does (barely adequately) work when there is manifold heat.
Great thanks. Should i just leave them as is? I’ll have to get car on jacks when its warmer too see what the exhaust is. ( i only drive the car in the summer/spring months on the easy coast)
If you want to drive it in cooler weather take the rear (over the exhaust) apron off- it will let some pre-heated air recirculate and maybe keep the carb from icing up. You'll have to keep an eye on engine temps, though. Of course, the proper solution is an exhaust with heat riser flanges.
A friend with a stock '74(?) Beetle takes the apron off in the fall, throws it behind the rear seat, re-installs it in the spring, claims way faster warm ups, higher operating temps to the point that the oil never gums up from not getting hot enough and way better interior heat.
So after getting under the car , should i just drill holes and connect them?
am i loosing hp or getting car fumes trapped in the engine bay?
You can purchase or fabricate block-off plates for the heat riser flanges.
That is assuming you're running either dual carbs or some different style of center manifold.
If it's a stock VW manifold, you want the risers from the exhaust connected to the intake manifold. Use the gaskets in the VW engine rebuild kit or order them separately.
@356_2cool2slow posted:Great thanks. Should i just leave them as is?
If it's not broken, don't fix it.
@356_2cool2slow posted:So after getting under the car , should i just drill holes and connect them?
am i loosing hp or getting car fumes trapped in the engine bay?
If you never have problems with carburetor/manifold icing (you'll know it when it won't hold idle without your foot on the gas pedal helping it and won't run worth crap until close to 3,000 rpm) then, as Stan said, don't worry about it. Some time when you have the rear (over the exhaust) apron off take a close look at the flanges on the exhaust- if there's a hole into the header then it should be capped off or connected to the heat riser portion of the intake manifold. If there's no hole then there's no escaping gases to worry about. Should you ever decide that the engine needs manifold heat, the common solution is to drill a 3/16" or so hole in the header on the right (passenger) side- those flanges on aftermarket exhausts aren't usually opened up, so if you're running a single carburetor you have to do it yourself. A VW mechanic friend once told me not to drill both sides as you don't want cross-flow from 1 side to the other. Hope this helps. Al
You say it's running fine, so unless you don't like the look of them I would leave them alone. They are not hurting anything as-is unless you want to drive it under 50F outside.
If, when you get under there to inspect your exhaust system, you find that your exhaust system has the matching flanges for the manifold heaters (and, if so, they probably have block-off plates covering them), you could connect them (there is a special gasket involved but they're cheap). However, from your photo I really doubt that there will be similar flanges on the exhaust system. From your photo, you don't have openings in the tinwork to allow them to pass through, but check the exhaust for flanges, anyway. Yah nevah know.
If no exhaust flanges, just live with it till you decide on dual carburetors (that don't have that pre-heater tube) or a different exhaust with heat riser flanges included or a different single-carb intake manifold without pre-heater.
Those are your options.
@Stan Galat posted:If it's not broken, don't fix it.
Just got the car so I guess I'll find out this spring with putting some miles on her.
